Phenol resins are used as caking additives in Example 1 of the method for forming molds shown in the Official Gazette of Japanese Patent Early publication (Kokai) No. Hei. 05-32148, and volatile gases such as formaldehyde, phenol and ammonia are generated when binders are cured by the heat of formed dies. The gases generated cause discomforting odors and have bad effects on human bodies. Or water glasses are used as in Example 2, and it is not preferable that molds after casting become refuse, because they cannot be recycled.
Also, a so-called forming method for shell molds, in which sand coated with binders is blown and filled in heated dies for forming and the filled binders coated with sand are cured by the heat of the dies, is disclosed in the Official Gazette of Japanese Patent Early-publication (Kokai) No. Hei. 10-193033.
Volatile gases such as formaldehyde, phenol, and ammonia are generated when binders are cured by the heat of the dies in the method for forming shown in the references of the patent. The gases generated cause discomforting odors and have bad effects on human bodies. Also, when these dies are used for casting, for example, aluminum alloys and resin binders are not fully volatilized or decomposed, because the pouring temperature into molds is about 700° C. As a result, a core may not be easily removed from cast metal after the cast metal is cooled. Further, a water jacket core for producing aluminum castings for automobile engines is complicated in shape and is very thin. Thus, if the binders in the core are not completely baked and decomposed by the heat conduction from the poured and melted metal, it is difficult to remove the core sand from the castings.
Further, as shown in the Official Gazette of Japanese Patent Early-publication (Kokai) No. Sho. 59-47043, it is not preferable that a caking additive composition using multi-functional aldehyde, glyoxal, urea, etc., as cross linking agents be used for casting, because they may generate toxic gases such as formaldehyde.
Also, it is very difficult to continuously fill mixtures in a blow head into molds by the method for forming molds shown in the Official Gazette of Japanese Patent Early-publication (Kokai) No. Sho. 55-8328, because the unit particles of silica sand in the blow head aggregate to become bulky because of the method when casting sand that is combined with binders mainly composed of water and aqueous binders frozen and the frozen mixture is blow-filled into molds or during the period that lasts until the second blow-filling is done. Thus, these kinds of methods for forming molds have not been practically used.
Further, when a core for casting using aqueous binders is left under a high humidity, the core may be deformed and not maintain its shape because the aqueous binders generally absorb water and their bonds are weakened. There has been a problem in that water vapor is generated when the water component is heated and it induces bubbles when pouring metal, though the poured metal can be used for casting.